Platoon travel systems are generally known. For example, a patent document 1 (i.e., Japanese Patent Laid-Open No. 2009-157790) discloses a platoon travel system. The platoon travel system is equipped with a self-vehicle information acquisition processing unit with which the platoon travel system acquires self-vehicle information. A nearby-vehicle information acquisition processing unit acquires information about nearby vehicles, and a platoon organization processing unit retrieves a projection area of each self-vehicle from the self-vehicle information and nearby vehicles from the nearby-vehicle information. The platoon organization processing unit then organizes the platoon based on the retrieved projection areas of the respective vehicles. Further, in a patent document 2 (i.e., Japanese Patent Laid-Open No. 2009-157794), a similar projection-area based platoon organization is disclosed.
However, when a platoon is based on the projection area of each of the vehicles, the platoon may temporarily collapse when a vehicle joins the platoon or when a vehicle departs from the platoon. In other words, in the platoon travel of vehicles, a vehicle interval may be widened in order to make room for a joining vehicle or for a departure of a vehicle from the platoon, which leaves a vacant position. Therefore, in the platoon travel system, after a collapse of the platoon and before a re-organization/reconstruction of the platoon, the energy consumption of the whole platoon may increase. Further, if such re-organization/reconstruction is frequent, the increase of the energy consumption may further increase.
Further, the vehicles participating in the platoon may have respectively different travel outputs (e.g., different horsepower output from the respective vehicles for the travel of those vehicles). Therefore, in the above-mentioned platoon travel system, even when the platoon is organized based on the projection area of each of the vehicles, a low-power vehicle may sometimes be positioned in front of a high-power vehicle. In other words, a lead vehicle may have a higher power than a following vehicle in the above-mentioned platoon travel system. In the above situation, a “high travel output power” and a “low travel output power” regarding the output of the vehicle are used as relative terms, indicating that travel output powers are different from vehicle to vehicle.
Further, when the vehicles of different travel outputs travel with the same amount of travel resistance, the low travel output vehicles consume more energy than the high travel output vehicles. Therefore, when the low travel output vehicles are positioned in front of the high travel output vehicles, the energy consumption of the whole platoon may increase.
Furthermore, the vehicles participating in the platoon have respectively different remaining energies. Therefore, in the above-mentioned platoon travel system, even when the platoon is organized based on the projection area of each of the vehicles, vehicles having low remaining energy may be positioned in front of vehicles having high remaining energy. In the above, high and low regarding the remaining energies are used as relative terms, indicating that remaining energies are different from vehicle to vehicle. Therefore, in other words, in the above-mentioned platoon travel system, the lead vehicle may have lower remaining energy than the following vehicle. Thus, in such positioning of the vehicles, the low remaining energy vehicle may benefit from low energy consumption reduction effects (e.g., low fuel saving amounts) even in the platoon travel, with possibly little or no extended travel distance.